Multistarter fermentation of high sugar musts

Background and Aims The possibility to decrease wine volatile acidity (VA) is an important aspect in wine production. This applies in particular to wines that are produced from musts with high sugar concentration, where the osmotic pressure promotes an increase in acetic acid production by Saccharomyces cerevisiae. This study aimed to identify suitable yeast strains and fermentation temperature to undertake the alcoholic fermentation of high sugar musts. Methods and Results To lower VA during fermentation of high sugar musts, two non‐Saccharomyces yeast strains, Zygotorulaspora florentina and Starmerella bacillaris, were used in multistarter fermentations with S. cerevisiae at a fermentation temperature of 14 and 20°C. The fermentation temperature influenced the yeast behaviour and the composition of the two mixed fermentations. Conclusions Independent of fermentation temperature, the mixed fermentations with Z. florentina performed best to reduce VA. Significance of the Study Mixed fermentations with the non‐Saccharomyces yeast strains Z. florentina and S. bacillaris may represent a valuable approach for the fermentation of high sugar musts

A fast and simple method for wild yeast flora detection in winemaking

Francesca Comitini, Mariza Stringini, Manuela Taccari, Maurizio CianiDipartimento S.A.I.F.E.T. sez. di Microbiologia Alimentare, Industriale e Ambientale, Università Politecnica delle Marche, Ancona, ItalyAbstract: An easy technique for a fast determination of wild yeast population-colonizing grape must before fermentation is described. The mathematical relationship between viable cell number and oxygen consumption rate was determined using a simple pO2 electrode chamber. This relation was determined in pure cultures belonging to six yeast species related to wine environment and in natural samples of grape must collected at the time of the grape delivery in the wineries. Results indicated a significant relationship between oxygen consumption rate and viable cell count of the wine yeast species tested. The evaluation of natural grape must samples indicated that the presence at pre-fermentative of wide contaminant yeast flora at a level commonly believed responsible for uncontrolled microbiological process in winemaking (>106 CFU ml−1), was easily detected. Since the results are available in a short time, this method could be profitable used to detect the presence of contaminant level of wild yeasts reducing the risk of uncontrolled start fermentation that could compromise the quality of final product.Keywords: wild yeasts contamination, oxygen consumption, O2 prob

Screening of yeasts for growth on crude glycerol and optimization of biomass production

Out of 113 yeast strains tested, 45 grew on pure glycerol with growth rates ranging from 0.11 to 0.37 h−1. Twenty-three strains showed specific growth rates (h−1), biomass production and biomass yields higher or comparable to those on glucose which suggests that crude glycerol can be utilized as carbon source in yeast cultivation for biomass production. Response surface methodology was applied to optimize crude glycerol concentration and temperature for biomass production and yield by Yarrowia lipolytica (DiSVA C 12.1), Metschnikowia sp. (DiSVA 50), Debaryomyces sp. (DiSVA 45/9), and Rhodotorula mucilaginosa (DiSVA C 7.1). A biomass concentration of 25.7 g/l and a biomass yield of 0.92 g/g (Y/Xglyc) was obtained with Y. lipolytica DiSVA C 12.1 and with R. mucilaginosa DiSVA C 7.1, respectively. These results demonstrate the potential use of crude glycerol as carbon source in yeast cultivation and the yeast ability to convert low-value crude glycerol to added-value products

The occurrence of beer spoilage lactic acid bacteria in craft beer production

Beer is one of the world's most ancient and widely consumed fermented alcoholic beverages produced with water, malted cereal grains (generally barley and wheat), hops, and yeast. Beer is considered an unfavorable substrate of growth for many microorganisms, however, there are a limited number of bacteria and yeasts, which are capable of growth and may spoil beer especially if it is not pasteurized or sterile-filtered as craft beer. The aim of this research study was to track beer spoilage lactic acid bacteria (LAB) inside a brewery and during the craft beer production process. To that end, indoor air and work surface samples, collected in the brewery under study, together with commercial active dry yeasts, exhausted yeasts, yeast pellet (obtained after mature beer centrifugation), and spoiled beers were analyzed through culture-dependent methods and PCR-DGGE in order to identify the contaminant LAB species and the source of contamination. Lactobacillus brevis was detected in a spoiled beer and in a commercial active dry yeast. Other LAB species and bacteria ascribed to Staphylococcus sp., Enterobaceriaceae, and Acetobacter sp. were found in the brewery. In conclusion, the PCR-DGGE technique coupled with the culture-dependent method was found to be a useful tool for identifying the beer spoilage bacteria and the source of contamination. The analyses carried out on raw materials, by-products, final products, and the brewery were useful for implementing a sanitization plan to be adopted in the production plant

Microbial Diversity of Type I Sourdoughs Prepared and Back-Slopped with Wholemeal and Refined Soft (Triticum aestivum) Wheat Flours

The fermentation of type I sourdough was studied for 20 d with daily back-slopping under laboratory and artisan bakery conditions using 1 wholemeal and 2 refined soft wheat (Triticum aestivum) flours. The sourdough bacterial and yeast diversity and dynamics were investigated by plate counting and a combination of culture dependent and culture-independent PCR-DGGE approach. The pH, total titrable acidity, and concentration of key organic acids (phytic, lactic, and acetic) were measured. Three flours differed for both chemical and rheological properties. A microbial succession was observed, with the atypical sourdough species detected at day 0 (i.e. Lactococcus lactis and Leuconostoc holzapfelii/citreum group for bacteria and Candida silvae and Wickerhamomyces anomalus for yeasts) being progressively replaced by taxa more adapted to the sourdough ecosystem (Lactobacillus brevis, Lactobacillus alimentarius/paralimentarius, Saccharomyces cerevisiae). In mature sourdoughs, a notably different species composition was observed. As sourdoughs propagated with the same flour at laboratory and artisan bakery level were compared, the influence of both the substrate and the propagation environment on microbial diversity was assumed

The occurrence of spoilage yeasts in cream-filled bakery products

BACKGROUND: Filling creams can provide an adequate substrate for spoilage yeasts because some yeasts can tolerate the high osmotic stress in these products. To discover the source of spoilage of a cream-filled baked product, end products, raw materials, indoor air and work surfaces were subjected to microbiological and molecular analyses. The efficacy of disinfectants against spoilage yeasts was also assessed. RESULTS: The analyses on end products revealed the presence of the closest relatives to Zygosaccharomyces bailii with counts ranging from 1.40 to 4.72 log cfu g−1. No spoilage yeasts were found in the indoor air and work surfaces. Polymerase chain reaction-denaturing gradient gel electrophoresis analysis, carried out directly on filling creams collected fromunopened cans, showed the presence of bands ascribed to the closest relatives to Z. bailii sensu lato, although with counts<1 log cfug−1. Susceptibility testing of yeast isolates to disinfectants showed a significantly lower effect of 10% alkyl dimethyl benzyl ammonium chloride. Different responses of isolates to the tested disinfectants were seen. CONCLUSION: To guarantee the quality of end products, reliable and sensitive methods must be used. Moreover, hygiene and the application of good manufacturing practices represent the most efficient way for the prevention and minimization of cross-contamination

Liquid sourdough from stone-ground soft wheat (Triticum aestivum) flour: development and exploitation in the breadmaking process

The aim of the study was to set up a liquid sourdough obtained using stone-ground soft wheat (Triticum aestivum) flour to be exploited in breadmaking. Therefore, a Type II sourdough (dough yield = 350) was developed from a stable stone-ground wheat Type I sourdough (dough yield = 156) used as inoculum. Both sourdoughs were analyzed for lactic acid bacteria (LAB) viable counts, pH and total titratable acidity (TTA), LAB biodiversity by a combined culture-dependent and -independent approach (PCR-DGGE) and they were tested for their breadmaking ability. In addition, the chemical and rheological features and volatile organic compounds of the stoneground soft wheat flour used in the experiment were investigated. The flour had a high protein content, good bakery properties and it also presented a rich aroma pattern characterized not only by the prevalence of green grass, flowery, and sweet aromas but also nutty, roasted and popcorn aromas. The sourdoughs I and II used in the trial were characterized by viable LAB counts, pH and TTA values typical of mature sourdoughs, i.e., approximately 9 log cfu gr-1 and mL, pH 3.9 and 10 mL 0.1 N NaOH. In addition, Levilactobacillus brevis and Companilactobacillus paralimentarius species represented the LAB stable microbiota of both sourdoughs. Both sourdoughs efficiently produce acceptable experimental breads characterized by different volatile profiles thus indicating that the type of sourdough fermentation significantly influenced the features of the final products. Overall, for the first time in the present study stone-ground wheat flour and bread have been characterized for their volatile aroma profile and sensory properties